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Rework XEdDSA signing policy: Compatible stops signing, AES-CCM overrides, Strict exemptions - #12191
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…ides Signing costs 66 bytes per packet. On a crowded mesh that matters, and packets on an AES-CCM channel were paying it on top of the CCM tag. Sending (perhapsEncode): - Compatible, the default, no longer signs. Balanced and Strict sign broadcasts as before; licensed (ham) nodes also sign unicasts, but now only under Balanced or Strict. - Packets on an AES-CCM (use_aead) channel are never signed. This also removes the case where a signed CCM packet passed signedDataFits() but then failed the CCM size check with TOO_LARGE. Receiving (checkXeddsaReceivePolicy): - Only Strict drops a packet for lacking a signature. Balanced no longer drops unsigned broadcasts from known signers; that downgrade rule and its canonical-sizing helper are removed. - An AES-CCM channel overrides Strict: its unsigned or unverifiable packets are accepted, since the CCM tag authenticates them. - A malformed or failing signature still drops the packet in every mode. Identity (new NodeDB::refusesUnsignedIdentity, used by updateUser, NodeInfoModule and TrafficManagementModule): - Balanced and Strict still refuse an unsigned NodeInfo that would change a known signer's identity, except on an AES-CCM channel. - Compatible accepts it, since firmware before 2.8 strips signatures when relaying. Channels::isAEADEnabled() now returns false for an out-of-range index instead of logging, since receive paths pass a packet's index unchecked. XEDDSA_SIGNATURE_FIELD_BYTES lost its only user and is removed. Tests: test_packet_signing drops the cases that pinned the removed downgrade sizing (A7-A9, A18-A19, E5, E10-E13, D1), flips A4 and E1 to acceptance, and adds AES-CCM, Compatible and ham cases (A18-A20, B18-B20, N12-N13). test_mqtt and test_traffic_management pin the same rules on the plaintext-MQTT and NodeInfo-cache paths. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
…o keys A NodeInfo request or reply carries the key a peer will use for PKI direct messages, but off ham mode only broadcasts were signed. A Strict node therefore dropped every NodeInfo reply and could only learn a new peer's key from a signed broadcast, hours apart. - perhapsEncode: under Balanced and Strict, NodeInfo is signed even when unicast (still never on an AES-CCM channel, never in Compatible). - TrafficManagementModule: a NodeInfo request that carries a signature is forwarded instead of answered from the cache. Its sender may need a signed reply, and a reply sent on the target's behalf can never be signed. - checkXeddsaReceivePolicy: a signed NodeInfo verified against a stored key must advertise that same key, and the key must hash to the sender's node number, as first contact already requires. Otherwise it is dropped. This stops a valid signature vouching for another key, and stops a key planted on trust under the wrong node number proving itself with fresh signatures. Tests: B7 now expects NodeInfo unicasts signed; B21 pins signing per policy; A21-A23 pin the key-consistency check; a traffic-management case pins that a signed request is forwarded while the same request unsigned is answered. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
Strict dropped every unsigned packet that was not PKI-encrypted. Acks and traceroutes are never signed, so a Strict node saw no acks, retransmitted every reliable packet to exhaustion, and could not take part in traceroutes. - checkXeddsaReceivePolicy: Strict no longer drops an unsigned ROUTING_APP packet; an ack carries its own proof (AckProof.h). Traceroutes are accepted in every mode, and any signature on one is ignored rather than verified. - perhapsEncode: a traceroute is never signed, including in ham mode, which signs other unicasts. Every relay rewrites the route, so a signature fails verification from the second hop on, and a bad signature drops the packet in every mode. - TraceRouteModule::alterReceivedProtobuf: strip any signature when rewriting the route, so a traceroute signed by older firmware is not dropped by older receivers further along. Tests: A24-A26 (Strict accepts unsigned acks and traceroutes; a traceroute signature is ignored), B22 (traceroutes never signed), B7 updated, and test_traceroute_nexthop pins the signature strip on rewrite. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
Only 2.8.0 and 2.8.1 pre-release nodes ever signed a traceroute: ham mode, which signs every unicast, and client-sent broadcast traceroutes. Stripping the signature on rewrite only helped those pre-releases interoperate, which does not justify the code. Receivers still ignore a traceroute signature, and traceroutes are still never signed. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
A position request or reply is PKI-excluded, so a signature is its only authentication, but off ham mode only broadcasts were signed. Strict dropped every position request and reply, and under Balanced any channel member could fake another node's location with an unsigned reply. perhapsEncode now signs POSITION_APP unicasts under Balanced and Strict, as it does NodeInfo. Nothing rewrites a position in flight - precision is applied by the originator before signing - so the signature survives relaying, and it binds request_id so a reply cannot be retargeted. Compatible and AES-CCM channels still sign nothing. Tests: B23 pins position unicast signing per policy and Strict acceptance; B7 expects position unicasts signed; B2 and B5 use PRIVATE_APP as their unsigned unicast now that position is signed. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
Key verification's bootstrap messages (M1, M2) go out channel-encrypted because the peer's key is not known yet, so they cannot carry a signature the receiver could verify. Strict dropped them, so two Strict nodes that did not already hold each other's keys could never run key verification. The handshake does not rely on the transport: hash1 binds both public keys to the security number the users exchange, and a key is only stored after the numbers match and the user accepts. A forged request can at most raise a verification prompt, bounded by the single session slot and the 60 s remote cooldown - as it already can under Balanced. Test: A27 pins that Strict accepts an unsigned key verification message. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
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Inline comments:
Review comments at @src/mesh/NodeDB.cpp:
- Around line 4409-4410: Use packet-level evidence of successful CCM
authentication instead of the channel’s AEAD setting in refusesUnsignedIdentity
and checkXeddsaReceivePolicy. Add a local-only packet flag set only after
decryptPacketCCM succeeds, clear it at ingress boundaries, and use it for both
unsigned-identity exemptions.
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src/mesh/Channels.cppsrc/mesh/CryptoEngine.hsrc/mesh/NodeDB.cppsrc/mesh/NodeDB.hsrc/mesh/Router.cppsrc/modules/NodeInfoModule.cppsrc/modules/TrafficManagementModule.cppsrc/mqtt/MQTT.cpptest/test_mqtt/MQTT.cpptest/test_packet_signing/test_main.cpptest/test_traffic_management/test_main.cpp
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Two cases expected updateUser() to refuse an unsigned update from a known signer under a zeroed config. Zeroed is Compatible, which now accepts it, so they failed in CI. Run them under Balanced, and add the Compatible counterpart so both halves of the rule are pinned at the updateUser level. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011DjtCrF8NLMGs9DtEVQkUK
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🔵 Needs a closer look
Authentication-policy changes need human security review and successful compilation and test results, which remain unverified.
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What changed in this PR
Reworks firmware packet authentication to avoid unnecessary signatures while retaining Strict enforcement and policy-aware identity protection.
Changes:
- Stops signing in Compatible mode and on AES-CCM channels; adds Strict exemptions.
- Centralizes unsigned identity checks and forwards signed NodeInfo requests instead of answering from cache.
- Updates regression tests for signing, identity, MQTT, and traffic management.
| File | Description |
|---|---|
test/test_traffic_management/test_main.cpp |
Tests identity guards and signed-request forwarding. |
test/test_packet_signing/test_main.cpp |
Updates signing and receive-policy coverage. |
test/test_nodedb_identity_hygiene/test_main.cpp |
Tests policy-dependent identity updates. |
test/test_mqtt/MQTT.cpp |
Tests revised unsigned downlink acceptance. |
src/mqtt/MQTT.cpp |
Updates policy comments only. |
src/modules/TrafficManagementModule.cpp |
Applies identity guard and forwards signed requests. |
src/modules/NodeInfoModule.cpp |
Uses shared identity policy. |
src/mesh/Router.cpp |
Revises signing, exemptions, and NodeInfo key checks. |
src/mesh/NodeDB.h |
Declares shared identity guard. |
src/mesh/NodeDB.cpp |
Implements policy-aware identity protection. |
src/mesh/CryptoEngine.h |
Removes unused signature-overhead constant. |
src/mesh/Channels.cpp |
Guards out-of-range AEAD lookups. |
Review effort: Balanced
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Is it possible, and what is the cost if it is, for trying messages to the same channel parameters (name, psk) for the non-aead equivalent when on an aead channel?
I'm still concerned that a single bool checkbox isn't enough to make it clear that a channel is wholly incompatible.
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@NomDeTom Yes, it's possible and cheap. But I'd use it to detect a mismatch, not to accept the packets. What happens today. An AES-CCM channel's hash is the plain channel's hash Cost of trying the plain variant. Only packets whose hash equals one of our CCM channels' hash Why detect rather than accept. Delivering a packet that only decrypted under plain AES-CTR would undo what AES-CCM is for: anyone with the PSK could send the unauthenticated version and have it accepted. When the plain variant decodes cleanly, the node would instead:
The reverse check works too, and is authenticated: a non-CCM node tries the CCM variant of its channels, and a valid CCM tag proves the peer holds the key. On the checkbox. Agreed that a bare bool undersells it. The channel URL already carries This PR doesn't change how AES-CCM channels are matched or decrypted; it only stops signing on them. So I'd keep the detection out of it and do it as a follow-up PR (firmware detection and notification, plus the app wording), if that works for you. Generated by Claude Code |
Summary
Reworks when packets are XEdDSA-signed and which unsigned packets are accepted. The aim is that each packet is authenticated by AES-CCM, PKI, or a signature, without paying for a 64-byte signature where it buys nothing. Companion protobufs comment update: meshtastic/protobufs#1141.
Sending (
perhapsEncode)use_aead) channel, whose tag already authenticates them. This also removes a case where a signed CCM packet passedsignedDataFits()and then failed the CCM size check withTOO_LARGE.Receiving (
checkXeddsaReceivePolicy)canonicalSignableSizehelper.AckProof.h);Identity
NodeDB::refusesUnsignedIdentity(), used byupdateUser,NodeInfoModuleandTrafficManagementModule. Balanced and Strict refuse an unsigned NodeInfo that would change a known signer's name or role, except on an AES-CCM channel. Compatible accepts it, since firmware before 2.8 strips signatures when relaying.TrafficManagementModuleforwards a signed NodeInfo request instead of answering it from cache: a reply sent on the target's behalf can never be signed.Other
Channels::isAEADEnabled()returns false for an out-of-range index instead of logging, since receive paths now pass a packet's index unchecked.XEDDSA_SIGNATURE_FIELD_BYTESremoved; the deleted Balanced size check was its only user.Rollout note
2.8.0 and 2.8.1 nodes still drop unsigned NodeInfo broadcasts from nodes that have signed before, and refuse their name changes, in every mode. Once upgraded nodes stop signing in Compatible, those older nodes will not see their name changes until they upgrade too.
Tests
test_packet_signing:test_mqtt: Balanced accepts unsigned plaintext downlink from a signer; Strict accepts it on an AES-CCM channel.test_traffic_management: the identity guard under Balanced, Compatible and an AES-CCM channel; a signed NodeInfo request is forwarded while the same request unsigned is answered.🤝 Attestations
Not yet tested. The native suites could not be built in the authoring environment: its network policy blocks the GitHub archive download PlatformIO needs for the native platform. The code was formatted with the pinned clang-format 20.1.0 and reviewed, but has not been compiled. Opened as a draft so CI runs the native suites first.
Generated by Claude Code
Summary by CodeRabbit
Security and Packet Handling
Identity Updates